1. Field of the Invention
The present invention relates to a method of manufacturing articles based on rubber and is applicable generally to rubber fabrication industries.
2. Description of the Prior Art
Industrial products exist which are entirely or partially based on rubber whose composition, structure and geometric shape are relatively complex.
Their manufacture assumes the use of materials which are different both in their nature and their composition. It is necessary, mostly, to form a blank from intermediate elements, to produce a well-defined final structure. This is followed lastly, by the final molding operation which simultaneously realizes two objectives, on the one hand, the almost final dimensional shaping of the product and, on the other hand, the vulcanization of the rubber mixes.
The forming of the blank assumes very considerable labor and fabricating means. The molding operation constitutes practically the last step in the manufacture.
The formation of the blank is an operation of assembling intermediate products of which the layout, carried out according to a given procedure, leads to the establishment of the final structure. It is important, at this stage of manufacture, to have intermediate products possessing good adhesion, that is to say the ability of each element to adhere or to stick to the structure in the course of fabrication without resorting to glueing agents. it is also important to have sufficient plasticity to insure ease of shaping by the action of stresses.
It must be noted that the plasticity of the elements is, to a very great extent, one of the most difficult problems to master in the production of intermediate products having dimensional characteristics which are both very accurate and very faithfully reproduced.
In the course of the molding operation, the vulcanization of the rubber mixes is carried out under the simultaneous action of time, temperature and pressure. This irreversible transformation modifies the physical and chemical properties of the initial mixes by conferring elasticity on them and causing the properties of adhesion and plasticity to practically disappear.
The molding operation always associates a dimensional shaping and a vulcanization, even partial, and hence a heat stabilizing of the product.
There are known to exist injection molding units for the fabrication of simple parts, in the sense that they use only a single rubber mix, but can be complex in their shape. The mix is introduced directly into the closed mold, through an injection nozzle, after plasticizing of the rubber mix. The advantage is the reduction in the time of vulcanization of the part since the injection temperature of the rubber is very close to its vulcanizing temperature.
Lastly, the adhesive power and plasticity of accelerated but unvulcanized rubbers and their capacity to preserve these properties as long as no vulcanization has taken place, are known.